I did an AS-level in history (didnt do the full A-level because i was planning to do a science at uni) about 6 years ago, i doubt its changed much since then.
If you liked the look of the content then imo that is the most important thing, half our course was British political history which i loved, so i enjoyed AS history a lot more than GCSE.
Imo it wasnt a paticularly difficult course - for each exam we were given 4 exam style questions at the start of the module, and told the exam question consisted of 2 questions which would be slight variants on the 4 given, so there were absolutely no surprises on any of the exams.
On the whole i found it very similar to the GCSE course, the main difference being that the exams consisted of a couple of longer essay style question rather than lots of shorter questions, you get a lot of practice writing essays throughout the course so you only have to be vaguely competant at that sort of thing going into the course. Another difference is that in the 2nd year of the A-level you spend a lot of time doing your personal study, we had the choice to do absolutely anything we wanted (i assume your school is the same), all my friends enjoyed this part as you can choose what you are most interested in, it is quite a lot of work though, you have to be prepared to read a lot of books on the topic if you want a good mark.
If i were you i'd go for it, if you like the look of the content you'll probably really enjoy it and be willing to put in the effort requied to get a good mark, and if you got a B at gcse in what sounds like a nightmare of class then you must be pretty good at it. Dont be put off if you dont really like essays, you quickly get used to them.